1. Field of the Invention
Aspects of the present invention relate to a multi-output power supply device, and more particularly, to a multi-output power supply device which, when power supplied to one output circuit of multiple output circuits is blocked, stably controls power output to other output circuits of the multiple output circuits.
2. Description of the Related Art
To obtain multiple output voltages from a low-capacity power supply device, a single converter using a single transformer is widely used to generate the multiple output voltages. Since the single converter only uses a single controller, the single converter employs a multi-output sensing (or feedback) circuit that observes and controls output of the multiple output voltages. However, when the feedback circuit is used for a power supply device that is able to switch off some of the multiple output voltages in order to reduce use of standby power during a standby mode, voltages of non-switched off output voltages cannot be controlled within a desired range.
FIG. 1 is a block diagram of a typical multi-output power supply device. Referring to FIG. 1, power is provided to a transformer 14 according to a switching operation of a first power switch 10 that is controlled by a first switch controller 12. The transformer 14 transforms the provided power according to its turn ratio and outputs a transformed power to a first output circuit 16 and a second output circuit 18. If required, the typical multi-output power supply device can have additional output circuits similar to the first output circuit 16 and a second output circuit 18 shown.
The first output circuit 16 outputs the transformed power supplied from the transformer 14 to a subsidiary load 24 and the second output circuit 18 outputs the transformed power to a second power switch 20 that switches the transformed power to a main load 26 according to a control of the second power switch 20. The respective transformed powers output from the first and second output circuits 16 and 18 pass through a feedback circuit 28 and are fed back as signals for controlling the first switch controller 12.
Power switching-off at a secondary side of the transformer 14 is used to restrain unnecessary load power consumption in or during the standby mode. In the standby mode, a standby mode controller of the subsidiary load 24 turns off the second power switch 20 to restrain power supply to the main load 26. Furthermore, in the standby mode, a value of the subsidiary load 24 is also minimized by a system power sequence, and the typical multi-output power supply device operates with the standby mode controller as a central element that senses an external interrupt to detect when the standby mode is converted into a normal mode.
When the typical multi-output power supply device is controlled using a single controller, however, an output voltage of a switched off output circuit from among the multiple output circuits of the power supply device cannot be observed (or determined) so that an error in controlling of the other output voltages is increased. This causes an output voltage error to deteriorate control characteristics of the typical multi-output power supply device and to excessively increase the output voltage of the power supply devices so as to destroy a load.